Belt unit, transfer unit including the belt unit, and image forming apparatus including the transfer unit

ABSTRACT

A belt unit includes a belt wound around a plurality of rollers to rotate endlessly, a contact member disposed along a surface of the belt, an opposing member disposed facing the contact member via the belt, a moving member including an action receiving portion, to swing and movably support the opposing member to contact and separate from the belt, and a moving assembly. The moving assembly includes an actuator to bias the action receiving portion in a first direction in which the opposing member contacts the belt and in a second direction opposite the first direction in which the opposing member separates from the belt, a drive mechanism to move the actuator in the first and the second directions, and an elastic member to transmit a moving force of the actuator to the action receiving portion when the actuator moves.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.13/137,667, filed on Sep. 1, 2011, which is based on and claims prioritypursuant to 35 U.S.C. §119 to Japanese Patent Application No.2010-199827, filed on Sep. 7, 2010, in the Japan Patent Office, theentire disclosure of each which is hereby incorporated herein byreference.

BACKGROUND

1. Field of the Invention

Example embodiments generally relate to an image forming apparatus, suchas a copier, a facsimile machine, a printer, or a multi-functionalsystem including a combination thereof, and more particularly, to a beltunit including a belt that contacts or separates from an object and animage forming apparatus including the belt unit.

2. Description of the Related Art

Related-art image forming apparatuses, such as copiers, facsimilemachines, printers, or multifunction printers having at least one ofcopying, printing, scanning, and facsimile functions, typically form animage on a transfer sheet such as a recording medium according to imagedata. Thus, for example, a charger uniformly charges a surface of animage bearing member; an optical writer projects a light beam onto thecharged surface of the image bearing member to form an electrostaticlatent image on the image bearing member according to the image data; adeveloping device supplies toner to the electrostatic latent imageformed on the image bearing member to render the electrostatic latentimage visible as a toner image; the toner image is directly transferredfrom the image bearing member onto a transfer sheet or is indirectlytransferred from the image bearing member onto a transfer sheet via anintermediate transfer member; a cleaning device then cleans the surfaceof the image carrier after the toner image is transferred from the imagecarrier onto the transfer sheet; finally, a fixing device applies heatand pressure to the transfer sheet bearing the unfixed toner image tofix the unfixed toner image on the transfer sheet, thus forming theimage on the transfer sheet.

In image forming apparatuses that employ a belt as an intermediatetransfer member (hereinafter referred to as an intermediate transferbelt), when transferring a toner image formed on a photoconductive drumonto the intermediate transfer belt, the intermediate transfer beltneeds to contact the photoconductive drum. However, if the intermediatetransfer belt remains in continuous contact with the photoconductivedrum, charge remaining on the intermediate transfer belt degrades thephotoconductive layer of the photoconductive drum, producing an unevenelectric potential on the photoconductive drum that results in unevenimages.

In a case of forming a monochrome image with a color image formingapparatus, only a photoconductive drum for the color black is used toform the monochrome image while other photoconductive drums remain idle.However, in order to prevent the intermediate transfer belt from gettingdamaged by friction with the photoconductive drums, it is necessary todrive the photoconductive drums for the color image even when thesephotoconductive drums are not actually used to form the image. As aresult, the lifespan of the photoconductive drums is shortened. Asimilar problem arises with a conveyance belt that transports arecording medium onto which a toner image is directly transferred fromthe photoconductive drums.

To address such a difficulty, there are known image forming apparatusesthat employ a belt unit including an eccentric cam to enable the belt tocontact and separate from the photoconductive drums.

However, such belt units are relatively large and expensive, thushindering efforts to provide the low-cost, compact image formingapparatuses for which there is market demand.

SUMMARY OF THE INVENTION

In view of the foregoing, in an example embodiment, a belt unit includesan endless rotatable belt, a contact member, an opposing member, amoving member, and a moving assembly. The endless rotatable belt iswound around a plurality of rollers and formed into a loop. The contactmember is disposed along a surface of the belt. The opposing member isdisposed facing the contact member via the belt. The moving memberswings and movably supports the opposing member to contact and separatefrom the belt. The moving member includes an action receiving portion.The moving assembly biases the action receiving portion of the movingmember in a first direction in which the opposing member contacts thebelt and in a second direction opposite the first direction in which theopposing member separates from the belt. The moving assembly includes anactuator, a drive mechanism, and an elastic member. The actuator biasesthe action receiving portion of the moving member in the first and thesecond directions. The drive mechanism moves the actuator in the firstand the second directions. The elastic member transmits a moving forceof the actuator to the action receiving portion when the actuator moves.

In another example embodiment, an image forming apparatus includes thebelt unit.

Additional features and advantages of the present invention will be morefully apparent from the following detailed description of illustrativeembodiments, the accompanying drawings and the associated claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description of exampleembodiments when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a schematic cross-sectional diagram illustrating an imageforming apparatus according to an example embodiment;

FIG. 2 is a schematic cross-sectional diagram illustrating anintermediate transfer belt unit employed in the image forming apparatusof FIG. 1, in a state in which an intermediate transfer belt contactsphotoconductive drums and primary transfer rollers;

FIG. 3 is a schematic cross-sectional diagram illustrating theintermediate transfer belt unit in a state in which the intermediatetransfer belt is separated from the photoconductive drums and theprimary transfer rollers;

FIG. 4 is a torque curve showing rotational torque of a cam shaft of aneccentric cam employed in the intermediate transfer belt unit as theprimary transfer rollers contact and separate from the intermediatetransfer belt;

FIGS. 5A through 5D are partially enlarged schematic diagramsillustrating a relation between an amount of rotation of the eccentriccam and positions of devices in the intermediate transfer belt unit inrelation to point A through point D shown in FIG. 4;

FIG. 6 is a schematic cross-sectional diagram illustrating a belt unitfor transporting a transfer sheet such as a recording medium, employedin an image forming apparatus, according to another example embodiment;

FIG. 7 is a schematic cross-sectional diagram illustrating a related-artbelt unit in an image forming apparatus;

FIG. 8 is a torque curve showing rotational torque of a cam shaft of aneccentric cam employed in the belt unit of FIG. 7 as primary transferrollers contact and separate from an intermediate transfer belt, and

FIGS. 9A through 9D are partially enlarged schematic diagramsillustrating a relation between an amount of rotation of the eccentriccam and positions of devices in the belt unit of FIG. 7 in relation topoint A through point D shown in FIG. 8.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

A description is now given of example embodiments. It should be notedthat although such terms as first, second, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,it should be understood that such elements, components, regions, layersand/or sections are not limited thereby because such terms are relative,that is, used only to distinguish one element, component, region, layeror section from another region, layer or section. Thus, for example, afirst element, component, region, layer or section discussed below couldbe termed a second element, component, region, layer or section withoutdeparting from the teachings of the present invention.

In addition, it should be noted that the terminology used herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of the present invention. Thus, for example, asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Moreover, the terms “includes” and/or “including”, when usedin this specification, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groups thereof

In describing example embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected, and it is to be understood that eachspecific element includes all technical equivalents that operate in asimilar manner and achieve a similar result.

In a later-described comparative example, illustrative embodiment, andalternative example, for the sake of simplicity, the same referencenumerals will be given to constituent elements such as parts andmaterials having the same functions, and redundant descriptions thereofomitted.

Typically, but not necessarily, paper is the medium from which is made asheet on which an image is to be formed. It should be noted, however,that other printable media are available in sheet form, and accordinglytheir use here is included. Thus, solely for simplicity, although thisDetailed Description section refers to paper, sheets thereof, paperfeeder, etc., it should be understood that the sheets, etc., are notlimited only to paper, but includes other printable media as well.

In order to facilitate an understanding of the related art and of thenovel features of the present invention, a description is provide of arelated-art belt unit employed in an image forming apparatus. FIG. 7 isa cross-sectional view of the related art belt unit.

An intermediate transfer belt unit 200 includes an intermediate transferbelt 210 formed into a loop, and four photoconductive drums 205B, 206M,206C, and 206Y An intermediate transfer belt unit 200 is a tandem-typeimage forming apparatus in which four photoconductive drums 205, 206M,206C, and 206Y, one for each of the colors black, magenta, cyan, andyellow are arranged in tandem. Primary transfer rollers 214, 215M, 215C,and 215Y are disposed inside the loop formed by the intermediatetransfer belt 210 opposite the photoconductive drums 205, 206M, 206C,and 206Y via the intermediate transfer belt 210. The primary transferroller 214 is swingably supported by an arm 216 and biased against theintermediate transfer belt 210 by a pressing spring 217. The primarytransfer rollers 215M, 215C, and 215Y are swingably supported by arms218M, 218C, and 218Y and biased by pressing springs 221M, 221C, and 221Yagainst the intermediate transfer belt 210. A moving assembly 230 movesthe primary transfer rollers 215 away from the intermediate transferbelt 210.

It is to be noted that the suffixes M, C, Y, and K denote colorsmagenta, cyan, and black, respectively. To simplify the description, thesuffixes M, C, Y, and K indicating colors are omitted herein, unlessotherwise specified.

The arms 218 are swingable about support shafts 219, thereby contactingor separating from the intermediate transfer belt 210. One end of eachof the pressing springs 221 contacts the rear end of the arms 218 (alsoreferred to as arm hook portions 220) while the other end of thepressing springs 221 is supported by a spring bearing surface 222 fixedto a frame, not illustrated, of the intermediate transfer belt unit 200.

The moving assembly 230 includes an eccentric cam 242, a slider 231, anda driving device 240 that drives the slider 231. The slider 231 moves tobias the arm hook portions 220 so that the primary transfer rollers 215can contact and separate from the intermediate transfer belt 210. Theslider 231 includes slider hook portions 232Y 232C, and 232M and a cambearing surface 233. The slider hook portions 232 directly contact thearm hook portions 220. The cam bearing surface 233 contacts a camsurface of the eccentric cam 242. The center of rotation of theeccentric cam 242 is connected to the driving device 240 via atransmitter 241 such as a gear and a pulley.

The eccentric cam 242 is rotated by the driving device 240, enabling theslider 231 to move and contact the aim hook portions 220. Accordingly,the aims 218 rotate about the support shafts 219, and the primarytransfer rollers 215 start to separate from the intermediate transferbelt 210. The pressing springs 221 are compressed as the slider 231moves, generating load torque in a direction hindering the rotation ofthe eccentric cam 242. When the primary transfer rollers 215 areseparated completely, an amount of compression is at maximum.

With reference to FIGS. 8 and 9A-9D, a description is provided of arelation between an amount of rotation of the eccentric cam and theposition of devices in the belt unit. FIG. 8 is a torque curve showing arotational torque of a cam shaft of the eccentric cam 242 when theprimary transfer rollers 215 contact and separate from the intermediatetransfer belt 210. FIGS. 9A through 9D are schematic diagramsillustrating positions of the devices associated with the amount ofrotation of the eccentric cam 242 shown in FIG. 8. It is to be notedthat in FIG. 9B through 9D, the suffix M indicating the color isomitted.

In FIG. 8, at point A, a bottom dead center 244 of the eccentric cam 242and the cam bearing surface 233 are closest to each other. In FIG. 8, atpoint C, a top dead center 243 of the eccentric cam 242 and the cambearing surface 233 contact each other. From point A to point B, theprimary transfer rollers 215 move in the direction separating from theintermediate transfer belt 210, but the primary transfer rollers 215 arestill in contact with the intermediate transfer belt 210. From point Bto point D, the primary transfer rollers 215 are separated from theintermediate transfer belt 210. From point B to point C, the primarytransfer rollers 215 move in the direction separating from theintermediate transfer belt 210. From point C to point D, the primarytransfer rollers 215 move towards the intermediate transfer belt 210.From point D to point A, the primary transfer rollers 215 move towardsthe intermediate transfer belt 210 and contact the intermediate transferbelt 210.

During color printing, the primary transfer rollers 215 are alwayspressed against the photoconductive drums 206. Hence, separating theprimary transfer rollers 215 from the intermediate transfer belt 210requires force greater than the pressing force. From point A to point B,a force F that the eccentric cam 242 receives from the slider 231 isF=F2×r. Therefore, the shaft torque in the direction opposite thedirection of rotation of the eccentric cam 242 is generated andcontinues to rise gradually. The shaft torque is at maximum near pointB, thus requiring relatively large drive torque, thereby complicatingefforts to make the driving device 240 as compact as is usually desired.From point B to point C, the torque decreases gradually, and change inthe torque becomes gradual near point C.

By contrast, from point C to point D, the slider 231 is pressed by thepressing spring 221 in the direction indicated by an arrow Ccorresponding to a direction of contact. In addition to the rotationaltorque (drive force) of the driving device 240, the force F (=F2×r)which accelerates rotation acts on the eccentric cam 242. As a result,engagement of the gear and the pulley becomes unstable due to backlashof the transmitter 241, hence generating undesirable noise such as shocksound when the gear or the pulley collides. After the acceleration ofthe eccentric cam 242 reaches the maximum (near point D), as the slider231 and the eccentric cam 242 collide and as the primary transfer roller215 and intermediate transfer belt 210 collide, undesirable shock soundis generated.

From point D to point A, the pressing force from the slider 231decreases gradually. Near point A, because the eccentric cam 242receives only rotational load from friction, engagement of the gear andthe pulley of the transmitter 241 becomes stable. In particular, inoffset transfer such as shown in FIG. 7, an amount of movement of theprimary transfer rollers 215 separating from the intermediate transferbelt 210 is large, and hence the amount of compression of the pressingspring 221 is large. This means that the force acting on the slider 231is also large. As a result, the shaft torque in the direction oppositethe direction of rotation of the eccentric cam 242 is large,necessitating large drive torque and hereby complicating efforts to makethe driving device 240 compact.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, andinitially to FIG. 1, one example of an image forming apparatus accordingto an example embodiment of the present invention is described.

FIG. 1 is a schematic cross-sectional diagram illustrating the imageforming apparatus according to the example embodiment. An image formingapparatus 100 is a tandem-type color image forming apparatus includingprocess cartridges 102Y, 102C, 102M, and 102BK arranged in tandem andremovably installable relative to the image forming apparatus 100. It isto be noted that the suffixes Y, C, M, and Bk denote colors yellow,cyan, magenta, and black, respectively. These suffixes indicating thecolors are omitted unless otherwise specified. The image formingapparatus 100 includes an exposure device 103, an intermediate transferunit 1 (hereinafter referred to as an intermediate transfer belt unit),a sheet cassette 104, a fixing device 110, and so forth.

Each of the process cartridges 102 includes a photoconductive drum(photoconductive drums 5, and 6Y, 6C, and 6M) serving as an imagebearing member and as a contact member. Substantially above the processcartridges 102, the exposure device 103 is disposed to illuminate thephotoconductive drums 5, and 6Y, 6C, and 6M with light. The exposuredevice 103 includes a light source such as a light-emitting diode (LED)and a laser diode (LD) to project light against the surfaces of thephotoconductive drums 5 and 6 based on a read image read by a readingunit, not illustrated, and an image signal sent from an external devicesuch as a personal computer and the like, thereby foil ling a latentimage on the surfaces of the photoconductive drums 5 and 6.

The sheet cassette 104 that stores multiple transfer sheets P (recordingmedia sheets) onto which a toner image is transferred is disposedsubstantially at the bottom of the image forming apparatus 100. Theimage forming apparatus 100 includes a sheet feed roller 105, a pair ofregistration rollers 107, a secondary transfer roller 109, the fixingdevice 110, and a sheet discharge tray 106. The sheet feed roller 105picks up a top sheet from a stack of transfer sheets P and sends it tothe downstream side in the direction of conveyance of the transfer sheetP. The secondary transfer roller 109 transfers the toner image onto thetransfer sheet P. The fixing device 110 fixes the toner image on thetransfer sheet P. After the toner image is fixed on the transfer sheetP, the transfer sheet P is discharged onto the sheet discharge tray 106.

The image forming apparatus 100 shown in FIG. 1 employs an intermediatetransfer method and includes the intermediate transfer belt unit 1serving as a belt unit. The intermediate transfer belt unit 1 includesan intermediate transfer belt 10 serving as an intermediate transfermember. The intermediate transfer belt 10 is formed into a loop androtates endlessly. The toner images formed on the photoconductive drums5 and 6 are primarily transferred onto the intermediate transfer belt 10and carried to the secondary transfer roller 109 where the toner imagesare transferred onto a recording medium.

After the secondary transfer process, a belt cleaning device 122 removesresidual toner that has not been transferred during the secondarytransfer process and thus remains on the intermediate transfer belt 10.The residual toner removed from the intermediate transfer belt 10 isrecovered to a waste toner bin 126. The belt cleaning device 122includes a cleaning blade 123 and a conveyance screw 124. The cleaningblade 123 contacts the intermediate transfer belt 10 to remove theresidual toner therefrom. The conveyance screw 124 transports theremoved toner to the waste toner bin 126.

The process cartridges 120 installed in the image forming apparatus 100forms toner images. The toner images are transferred primarily onto theintermediate transfer belt 10 so that they are superimposed one atop theother, thereby forming a composite toner image. Subsequently, thetransfer sheet P in the sheet cassette 104 is picked up and sent to thepair of registration rollers 107 by the sheet feed roller 105. The pairof registration rollers 107 stops the transfer sheet P temporarily andsends it to the secondary transfer roller 109 in appropriate timing suchthat the transfer sheet P is aligned with the composite toner imageformed on the intermediate transfer belt 10. Accordingly, the compositetoner image is transferred onto the transfer sheet P. Subsequently, thetransfer sheet P bearing the composite toner image passes betweenrollers of the fixing device 110 so that the composite toner image isfixed onto the transfer sheet P by heat and pressure. Subsequently, thetransfer sheet P is discharged onto a sheet discharge tray 106.

The residual toner remaining on the intermediate transfer belt 10, nothaving been transferred onto the transfer sheet P after the secondarytransfer, is removed by the cleaning blade 123, and transported as wastetoner to one end of the belt cleaning device 122 by the conveyance screw124. The waste toner passes through a joint portion 125 connected to thewaste toner bin 126 and is collected in the waste toner bin 126. Whilethe waste toner is collected in the waste toner bin 126, a mixing plate127 is vibrated to mix the waste toner in the waste toner bin 126 sothat the waste toner bin 126 is filled with the waste toner thoroughly.The mixing plate 127 contacts a shaft 128 penetrating from inside thewaste toner bin 126 to outside. A gear 129 provided to an end portion ofthe shaft 128 engages a gear 130 of the image forming apparatus 100 toreceive force generated by the vibration.

With reference to FIG. 2, a description is provided of the intermediatetransfer belt unit 1 employed in the image forming apparatus 100according to the illustrative embodiment of the present invention. FIG.2 is a schematic cross-sectional diagram illustrating the intermediatetransfer belt unit 1 in a state in which the intermediate transfer belt10 contacts the photoconductive drums 5 and 6M, 6C, and 6K, and primarytransfer rollers 14 and 15M, 15C, and 15Y. It is to be noted that thesuffixes Y, C, M, and Bk indicating colors are omitted unless otherwisespecified.

The intermediate transfer belt unit 1 (a belt unit) includes theintermediate transfer belt 10 (a belt member) formed into a loop andwound around and stretched between a drive roller 12 and a driven roller13 (stretch members). The photoconductive drums 5 and 6 serving as animage bearing member and as a contact member are disposed in tandemoutside the loop formed by the intermediate transfer belt 10 along thesurface of the intermediate transfer belt 10. The primary transferrollers 14 and 15M, 15C, and 15Y (opposing members) are disposed insidethe loop formed by the intermediate transfer belt 10, facing thephotoconductive drums 5 and 6.

The drive roller 12 is rotated by a driving device, not illustrated,thereby rotating the inteimediate transfer belt 10 in a directionindicated by an arrow A. The primary transfer roller 14 is supportedswingably by an arm 16 (moving member). The primary transfer rollers15Y, 15C, and 15M are supported swingably by arms 18Y, 18C, and 18Mserving as moving members, respectively. One end of the arm 16 supportsthe primary transfer roller 14. The other end the arm 16 is rotatableabout a shaft 16 a. A pressing spring 17 disposed at the primarytransfer roller side presses the primary transfer roller 14 against thephotoconductive drum 5.

One end of the aims 18 supports the primary transfer rollers 15. Theother end the arms 18 is rotatable about shafts 19Y, 19C, and 19M eachdisposed substantially at the center of the arms 18. Elastic members,such as pressing springs 51Y, 51C, and 51M, are disposed substantiallyat the other end of the arms 18 with a slot 20 and press the primarytransfer rollers 15 against the photoconductive drums 6.

The photoconductive drum 5 is used for forming an image of the colorblack. The photoconductive drums 6Y, 6C, and 6M are used for forming animage of the colors yellow, cyan, and magenta, respectively. With acombination of the photoconductive drums 5 and 6, an image of a singlecolor or an image of multiple colors is formed.

Although not illustrated, a charger, a developing device, aphotoconductive drum cleaner, and so forth are disposed around each ofthe photoconductive drums 5 and 6 in the clockwise direction. In theimage forming process, the chargers charge the surface of thephotoconductive drums 5 and 6. The developing devices develop latentimages formed on the photoconductive drums 5 and 6 with toner, therebyforming visible images, also known as toner images. Subsequently, thetoner images on the photoconductive drums 5 and 6 are transferred ontothe intermediate transfer belt 10 such that they are superimposed oneatop the other, thereby forming a composite toner image. After theprimary transfer process, residual toner remaining on thephotoconductive drums 5 and 6 is cleaned by the photoconductive drumcleaner. Alternatively, the photoconductive drum cleaner may beeliminated. This is known as a cleanerless method, in which thedeveloping device collects the residual toner. Still alternatively, aknown cleaning method may be employed.

According to the illustrative embodiment, a bias is supplied to theprimary transfer rollers 14 and 15 by a bias application device, notillustrated, thereby transferring electrostatically the toner imagesfrom the photoconductive drums onto the intermediate transfer belt 10.

According to the illustrative embodiment, the primary transfer methodemploys a roller-type primary transfer member, that is, the primarytransfer rollers 14 and 15. Alternatively, a brush-type primary transfermember may be employed.

The secondary transfer roller 109 is disposed opposite the drive roller12 via the intermediate transfer belt 10, thereby forming a secondarytransfer nip therebetween. The transfer sheet P is transported to thesecondary transfer nip between the intermediate transfer belt 10 and thesecondary transfer roller 109. The transfer sheet P passes through thesecondary transfer nip. The composite color toner image on theintermediate transfer belt 10 is transported to the secondary transfernip between the intermediate transfer belt 10 and the secondary transferroller 109. As the transfer sheet P passes through the secondarytransfer nip, the composite toner image is transferred secondarily ontothe transfer sheet P.

The drive roller 12 may be supplied with a bias same as the polarity oftoner by the bias application device so that the composite toner imageis electrostatically and secondarily transferred onto the transfer sheet(known as repulsive transfer). Alternatively, the secondary transferroller 109 may be supplied with a bias opposite the polarity of thetoner so that the composite toner image is electrostatically andsecondarily transferred onto the transfer sheet (known as attractivetransfer).

After the secondary transfer, the transfer sheet P passes through thefixing device 110 shown in FIG. 1 in which the toner image is fixed onthe transfer sheet P, thereby forming an output image. Alternatively,heat is applied to the toner image on the transfer sheet P so thattransfer and fixation of the toner image are performed at the same time.

With reference to FIGS. 2 and 3, a description is provided of the beltunit, here, the intermediate transfer belt unit 1, according to theillustrative embodiment of the present invention. FIG. 3 is a schematiccross-sectional diagram illustrating the intermediate transfer belt unit1 in a state in which the intermediate transfer belt 10 is separatedfrom the photoconductive drums 5 and 6, and the primary transfer rollers14 and 15.

It is to be noted that the suffixes Y, C, M, and Bk indicating colorsare omitted unless otherwise specified.

In FIG. 2, the intermediate transfer belt 10 is in contact with thephotoconductive drums 6 and the primary transfer rollers 15. Bycontrast, in FIG. 3, the photoconductive drums 6 and the primarytransfer rollers 15 are separated from the intermediate transfer belt10. As illustrated in FIGS. 2 and 3, in the intermediate transfer beltunit 1, the photoconductive drums 6 and the primary transfer rollers 15can contact and separate from the intermediate transfer belt 10.

According to the illustrative embodiment, the intermediate transfer beltunit 1 includes the pressing springs 51Y, 51C, and 51M to press the arms18Y, 18C, and 18M, respectively. Each of the arms 18 includes the slot20 which is an action receiving portion at the rear end portion thereof.As illustrated in FIGS. 2 and 3, the intermediate transfer belt unit 1includes a moving assembly 30. The moving assembly 30 enables theprimary transfer rollers 15 to contact the intermediate transfer belt 10when the arms 18 are pressed through the slots 20. The moving assembly30 enables the primary transfer rollers 15 to separate form theinteiinediate transfer belt 10 when the arms 18 are released (notpressed).

The moving assembly 30 includes a slider 31 serving as an actuator, adriving device 40 serving as a drive source, an eccentric cam 42 servingas a drive mechanism, and the pressing springs 51Y, 51C, and 51M as anexample of an elastic member. The slider 31 moves reciprocally between afirst position shown in FIG. 2 and a second position shown in FIG. 3.When the moving assembly 30 moves to the first position, the rear endportion of the arms 18 is biased in the direction indicated by an arrowC (a contact direction). When the moving assembly 30 moves to the secondposition, the rear end portion of the arms 18 is biased in the directionindicated by an arrow B (a separation direction). The driving device 40enables the slider 31 to move. The eccentric cam 42 converts the driveforce (rotary force) of the driving device 40 into reciprocal movement.The pressing springs 51 transmit the moving force of the slider 31 tothe rear end portion of the arms 18.

The slider 31 includes slider hook portions 32Y, 32C, and 32M, cambearing surfaces 33 and 34, and spring bearing surfaces for the pressingsprings 51. The slider hook portions 32Y, 32C, and 32M press the rearend portions of the aims 18 via the pressing springs 51. The cam bearingsurfaces 33 and 34 are disposed facing each other via the eccentric cam42 and contact a cam surface of the eccentric cam 42.

The driving device 40 is, for example, a drive motor. The drive force ofthe driving device 40 is transmitted to the eccentric cam 42 by atransmitter 41 including a gear, a pulley, and so forth. The eccentriccam 42 is rotated by the drive force of the driving device 40.

The pressing springs 51 are disposed at the rear end side of the arms 18and held elastically in connectors 52Y, 52C, and 52M. One end of thepressing springs 51 at the arm side is supported by bearing surfaces 52aY, 52 aC, and 52 aM of the connectors 52. The other end of the pressingsprings 51 is supported by a bearing surface of the slider hook portions32 of the slider 31. One end of each of the connectors 52 includes asupport pin 53 that fits into the hole 20. The other end of theconnectors 52 includes a bearing surface 54 that contacts the sliderhook portion 32 when the slider 31 is at the second position.

As illustrated in FIGS. 2 and 3, the connectors 52 and the slider 31 aredisposed substantially near the arms 18. The connectors 52 and theslider 31 move in the same direction. That is, the connectors 52 and thepressing springs 51 in the connectors 52 move in the same direction asthe direction of movement of the slider 31. In particular, in a sate inwhich the primary transfer roller 15 is separated from the intermediatetransfer belt 10, an amount of movement of the connector 52 and thepressing spring 51 equals the amount of movement of the slider 31.

The support pin 53 of the connector 52 is rotatably supported by thehole 20 of the arm 18. The arm 18 is pressed by the pressing spring 51disposed between the end surface (a spring bearing surface) of theslider hook portion 32 at the arm side and the connector 52. The bearingsurface 54 of the connector 52 is disposed facing the pressing spring 51via the slider hook portion 32 of the slider 31. In a state in which theprimary transfer roller 15 contacts the intermediate transfer belt 10 asillustrated in FIG. 2, the bearing surface 54 of the connector 52 isseparated from the slider hook portion 32.

The slider 31 includes the cam bearing surfaces 33 and 34 such that theeccentric cam 42 is disposed therebetween. Rotating the driving device40 connected to the eccentric cam 42 through the transmitter 41 such asthe gear and the pulley in one direction enables the slider 31 to movereciprocally in the directions indicated by arrows B and C.

Rotating the eccentric cam 42 from the state illustrated in FIG. 2enables the slider 31 to move in the direction of arrow B while beingpressed by the pressing spring 51. As the eccentric cam 42 is rotatedfurther, the eccentric cam 42 contacts the cam bearing surface 33,moving the slider 31 in the direction of arrow B. The connector 52 movesin the direction of arrow B in conjunction with the slider 31, rotatingthe arm 18 about the support shaft 19. Accordingly, the primary transferroller 15 moves away from the photoconductive drum 6, that is, theprimary transfer roller 15 separates from the intermediate transfer belt10.

As the top dead center 43 of the eccentric cam 42 comes to a position atwhich the top dead center 43 contacts the cam bearing surface 33 of theslider 31, rotation of the eccentric cam 42 is stopped. The intermediatetransfer belt 10 and the photoconductive drum 6 are separated completelyas illustrated in FIG. 3. By contrast, as the eccentric cam 42 isrotated in a state in which the intermediate transfer belt 10 and thephotoconductive drum 6 are separated as illustrated in FIG. 3, theeccentric cam 42 contacts the cam bearing surface 34, thereby moving theslider 31 in the direction of arrow C.

The connector 52 also moves in the direction of arrow C, rotating thearm 18 and hence moving the primary transfer roller 15 to contact theintermediate transfer belt 10. Then, the primary transfer roller 15stops. As the eccentric cam 42 is rotated further, the slider hookportion 32 separates from the bearing surface 54. As a result, thepressure of the pressing spring 51 acts on the slider 31 and the arm 18such that the slider 31 pushes back the eccentric cam 42, and the arm 18moves the primary transfer roller 5 towards the photoconductive drum 6.As the top dead center 43 of the eccentric cam 42 comes to a position atwhich the top dead center 43 contacts the cam bearing surface 34 of theslider 31, rotation of the eccentric cam 42 is stopped. Accordingly, theintermediate transfer belt 10 and the photoconductive drum 6 contacteach other as illustrated in FIG. 2.

According to the illustrative embodiment, as is understood from FIGS. 2and 3, a perpendicular line from the center of rotation of thephotoconductive drum 6 to the surface of the intermediate transfer belt10 wound around the drive roller 12 and the driven roller 13 does notoverlap with a perpendicular line from the center of the primarytransfer roller 15 to the surface of the intermediate transfer belt 10.The primary transfer roller 15 pushes up the intermediate transfer belt10 such that the intermediate transfer belt 10 is wound around a portionof the photoconductive drum 6. In other words, the position of theprimary transfer roller 15 is shifted relative to the photoconductivedrum 6 in the direction of movement of the intermediate transfer belt10. Accordingly, the primary transfer roller 15 pushes up theintermediate transfer belt 10 so that the intermediate transfer belt 10is wound around a portion of the photoconductive drum 6.

The position of the primary transfer roller 15 relative to thephotoconductive drum 6 when contacting the photoconductive drum 6 isfixed, and the primary transfer roller 15 is not biased against thephotoconductive drum 6. In this configuration, such as an offsettransfer method, the primary transfer roller 15 tends to move by a largeamount when contacting or separating from the photoconductive drum 6,hence necessitating a large eccentric amount of the eccentric cam 42.The large eccentric amount of the eccentric cam 42 increases frictionalforce between the eccentric cam 42 and the slider 31. As a result, therotational torque of the cam shaft is likely large.

In view of the above, according to the illustrative embodiment, therotational torque of the cam shaft can be reduced in the belt unithaving the moving mechanism of the present invention. In particular, itis advantageous to employ the present invention in the belt unit usingthe offset transfer method.

With reference to FIGS. 4 and 5, a description is provided of rotationaltorque of the cam shaft of the eccentric cam. FIG. 4 is a torque curveshowing the rotational torque of the cam shaft of the eccentric cam 42when the primary transfer rollers 15 contact/separate from theintermediate transfer belt 10. FIGS. 5 A through 5 D are partiallyenlarged schematic diagrams illustrating a relation between an amount ofrotation of the eccentric cam 42 and positions of devices in theintermediate transfer belt unit 1 in relation to point A through point Dof FIG. 4. In FIGS. 5 B through 5 D, the suffix M indicating the coloris omitted.

From point A to point B in FIG. 4, a pressing force F3 of the pressingspring 51 in addition to the rotational torque of the eccentric cam 42acts on the eccentric cam 42 so that engagement of the gear and thepulley of the transmitter 41 is unstable as in the related art. However,an amount of compression of the pressing spring 51 is significantlysmall, when compared with the related art, thereby reducingsignificantly the shock noise.

At point B, the slider hook portion 32 and the bearing surface 54contact each other, and the pressing spring 51 is stretched between thebearing surface 52 a and the bearing surface 54, with the slider hookportion 32 therebetween. As a result, the pressing force F3 against theslider 31 and the arm 18 becomes zero. From point B to point C, inaddition to the load torque of the driving system such as the drivingdevice 40 and the transmitter 41, the weight of the slider 31 and eachpart connecting to from the slider 31 to the primary transfer roller 15,and resultant force of the load torque due to friction act on theeccentric cam 42 so that the force in the direction of acceleration ofthe eccentric cam 42 acts on the eccentric cam 42. However, the pressingforce is significantly smaller than the pressing force from point A topoint B. Hence, the shock noise can be small.

On the contrary to point B to point C, from point C to point D, the loadtorque opposite the direction of rotation of the eccentric cam 42 actson the eccentric cam 42. From point D to point A in a state in which theprimary transfer roller 15 contacts the intermediate transfer belt 10,in addition to the load torque opposite the direction of rotation of theeccentric cam 42, the pressing spring 51 presses the slider 31. Ascompared with the related art, the amount of movement of the slider 31pressing the arm 18 is significantly small, thereby reducing the drivingtorque and hence the size of the driving device 40 and the transmitter41.

The slider hook portion 32 of the slider 31 serves as the bearingsurface for the pressing spring 51 and the hook for rotating the arm 18.In this configuration, the moving mechanism 30 can be made compact.According to the illustrative embodiment, the slider hook portion 32,the slider 31, and the pressing spring 51 move together during thecontact/separation operation of the primary transfer roller 15.Accordingly, compression of the pressing spring 51 accompanied by themovement of the slider 31 occurs only when the primary transfer roller15 contacts the intermediate transfer belt 10, thereby reducingfluctuation of the load torque relative to the cam shaft of theeccentric cam 42. With this configuration, the rotational torquerequired for the driving device 40 and the shock noise when the primarytransfer roller 15 contacts or separates from the intermediate transferbelt 10 are reduced, if not prevented entirely.

Furthermore, the moving mechanism 30 can be made compact by having theslider hook portion 32 to serve as both the bearing surface for thepressing spring 51 and the hook portion for rotating the arm 18. Thecost can be also reduced.

According to the illustrative embodiment, the pressing spring 51 doesnot press directly the arm 18, but presses the arm 18 via the connector52. In a case in which the arm 18 is pressed directly by the pressingspring 51, a spring bearing surface needs to be provided to the rear endof the arm 18. Generally, the spring bearing surface has a flat surface.If the spring bearing surface provided to the arm 18 is tilted due torotation of the arm 18, the pressing spring 51 buckles. Thus, some extraspace is needed to allow buckling of the pressing spring 51.

In view of the above, according to the illustrative embodiment, thepressing spring 51 presses the arm 18 via the connector 52 so that thepressing spring 51 is prevented from buckling, hence reducing the sizeof the moving mechanism 30.

According to the illustrative embodiment, the support pin 53 of theconnector 52 is fitted into the hole 20 of the arm 18. With thisconfiguration, force is transmitted from the connector 52 to the arm 18in both cases in which the primary transfer roller 15 contacts theintermediate transfer belt 10 and it separates from the intermediatetransfer belt 10.

If the arm 18 and the connector 52 are not connected, when moving theprimary transfer roller 15 towards the intermediate transfer belt 10,force from the connector 52 acts on the arm 18. On the other hand, whenseparating the primary transfer roller 15 from the intermediate transferbelt 10, no force from the connector 52 acts on the arm 18. As a result,when the primary transfer roller 15 is separated from the intermediatetransfer belt 10, the arm 18 separates from the connector 52. When theprimary transfer roller 15 contacts the intermediate transfer belt 10,the arm 18 contacts the connector 52, producing the shock noiseundesirably. Due to the shock noise, the product value is degraded.

In view of the above, according to the illustrative embodiment,connecting the arm 18 and the connector 52 prevents undesirable shocknoise upon moving the primary transfer roller 15. Hence, the productvalue is enhanced. Furthermore, because the hole 20 is a slot, theconnector 52 does not move vertically when the rear end portion of thearm 18 moves in the shape of arc of a circle about the support shaft 19.Accordingly, the primary transfer roller 15 is moved reliably.

Still further, the slider 31 includes the cam bearing surface 33disposed opposite the cam surface 34 via the eccentric cam 42. Withoutthe cam bearing surface 33, that is, having the cam surface 34 only, thedrive force from the eccentric cam 42 acts only in the direction ofarrow C. In this case, when the primary transfer roller 15 is separatedfrom the intermediate transfer belt 10, the eccentric cam 42 and the camsurface 34 are separated. As the drive force of the eccentric cam 42acts on the cam bearing surface 34 again, the eccentric cam 42 strikesthe cam bearing surface 34, producing shock noise.

By contrast, without the cam bearing surface 34, that is, having onlythe cam surface 33, a biasing force enabling the primary transfer roller15 to contact the intermediate transfer belt 10 is necessitated.However, when separating the primary transfer roller 15 from theintermediate transfer belt 10, the primary transfer roller 15 needs tomove against the biasing force, requiring greater rotational torque ofthe eccentric cam 42. To address this difficulty, the slider 31 includestwo cam bearing surfaces 33 and 34.

According to the illustrative embodiment, the intermediate transfer belt10 contacts and separates from the photoconductive drum 6 by moving theprimary transfer roller 15. Alternatively, the photoconductive drum 6may move to contact and separate from the intermediate transfer belt 10.

With reference to FIG. 6, a description is provided of a belt unitaccording to another illustrative embodiment of the present invention.

FIG. 6 is a schematic cross-sectional diagram illustrating a belt unitfor transporting a transfer sheet or a recording medium and an imageforming apparatus employing the belt unit. According to the presentembodiment, the intermediate transfer belt unit 1 is employed as a beltunit for transporting a transfer sheet. It is to be noted that the samereference numerals used in the foregoing embodiments are provided to thesimilar or the same constituent elements in FIG. 6 when discriminationtherebetween is not required. The suffixes Y, C, M, and Bk indicatingcolors are omitted unless otherwise specified.

According to the foregoing embodiment, a description is provided of thebelt unit employed in the tandem-type image forming apparatus using theintermediate transfer method. Alternatively, the belt unit may beemployed in the tandem-type image forming apparatus using adirect-transfer method. Here, in the image forming apparatus using adirect-transfer method a toner image formed on a photoconductive drum istransferred directly to a transfer sheet or a recording medium.

In FIG. 6, a belt unit 2 for transporting the transfer sheet or therecording medium includes a transfer sheet conveyance belt 11 (a beltmember) formed into a loop and wound around and stretched between thedrive roller 12 and the driven roller 13. The photoconductive drums 5,6M, 6C, and 6Y (contact members) are disposed in tandem outside the loopformed by the transfer sheet conveyance belt 11 along the surfacethereof. Transfer rollers 61, 62M, 62C, and 62Y (opposing members) aredisposed inside the loop formed by the transfer sheet conveyance belt11, facing the photoconductive drums 5, 6M, 6C, and 6Y, respectively.

The transfer sheet P is transported on the transfer sheet conveyancebelt 11 while being sandwiched between the photoconductive drums 5, 6M,6C, and 6Y, and the transfer sheet conveyance belt 11, therebytransferring the toner images borne on the photoconductive drums 5, 6M,6C, and 6Y onto the transfer sheet P. In FIG. 6, the center of rotationof the transfer rollers 61 and 62 is immediately below the center ofrotation of the photoconductive drums 5 and 6. In other words, aperpendicular line from the center of rotation of the photoconductivedrums 5 and 6 to the transfer sheet conveyance belt 11 wound around thedrive roller 12 and the driven roller 13 is aligned with the center ofrotation of the transfer rollers 61 and 62.

Alternatively, similar to the foregoing embodiment, the image formingapparatus may employ the offset-transfer method in which the transferrollers 61 and 62 are disposed such that the transfer sheet conveyancebelt 11 is wound around a portion of the photoconductive drums 5 and 6.

According to example embodiments, the transfer sheet conveyance belt 11contacts or separates from the photoconductive drum 6. Alternatively,the photoconductive drum 6 may move to contact and separate from thetransfer sheet conveyance belt 11. In such a configuration, the sameeffect as that of the foregoing embodiment can be achieved.

Example embodiments may be employed in the image forming apparatus. Theimage forming apparatus includes, but is not limited to, a copier, aprinter, a facsimile machine, and a multi-functional system.

Furthermore, it is to be understood that elements and/or features ofdifferent illustrative embodiments may be combined with each otherand/or substituted for each other within the scope of this disclosureand appended claims. In addition, the number of constituent elements,locations, shapes and so forth of the constituent elements are notlimited to any of the structure for performing the methodologyillustrated in the drawings.

Example embodiments being thus described, it will be obvious that thesame may be varied in many ways. Such exemplary variations are not to beregarded as a departure from the scope of the present invention, and allsuch modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. An image forming apparatus comprising: a belt; atransfer roller to come into contact with the belt; an arm to supportthe transfer roller; a connector connected to the arm; an actuator tomove the arm via the connector; and a spring, one end of the springbeing supported by the connector and the other end of the spring beingsupported by the actuator, wherein the connector is connected to the armby a pin and a slot into which the pin is inserted, wherein the transferroller separates from the belt when the actuator moves the arm, andwherein the actuator includes a slider, and the slider comes intocontact with the connector when the transfer roller separates from thebelt, and the slider separates from the connector when the transferroller comes into contact with the belt.
 2. The image forming apparatusaccording to claim 1, further comprising an eccentric cam to move theactuator linearly and a drive motor to drive the eccentric cam.
 3. Theimage forming apparatus according to claim 1, further comprising ashaft, wherein the transfer roller separates from the belt when theactuator causes the arm to rotate about the shaft.
 4. The image formingapparatus according to claim 1, wherein the connector and the slidermove in the same direction.
 5. The image forming apparatus according toclaim 4, wherein the connector and the spring move in the same directionas the direction of movement of the slider.
 6. The image formingapparatus according to claim 1, wherein the connector includes the pinand the arm includes the slot.
 7. The image forming apparatus accordingto claim 1, wherein the transfer roller comes into contact with an innersurface of the belt.
 8. An image forming apparatus comprising: a belt; atransfer roller to come into contact with the belt; an arm to supportthe transfer roller; a connector connected to the arm; an actuator tomove the arm via the connector; and a shaft, wherein the actuatorincludes a slider, the transfer roller separates from the belt when theslider slides linearly to cause the arm to rotate about the shaft,wherein the connector is connected to the arm by a pin and a slot intowhich the pin is inserted, and the transfer roller separates from thebelt when the actuator moves the arm, and wherein the transfer rollercomes into contact with an inner surface of the belt.
 9. The imageforming apparatus according to claim 8, wherein the pin moves relativeto the slot when the actuator moves the arm.
 10. The image formingapparatus according to claim 9, wherein the connector includes the pin,and the arm includes the slot.
 11. The image forming apparatus accordingto claim 9, wherein the pin comes into contact with one end of the slotwhen the transfer roller separates from the belt, and the pin comes intocontact with the other end of the slot when the transfer roller comesinto contact with the belt.
 12. The image forming apparatus according toclaim 8, further comprising an eccentric cam to move the slider linearlyand a drive motor to drive the eccentric cam.
 13. The image formingapparatus according to claim 8, wherein the connector moves in the samedirection as a direction of movement of the slider.
 14. The imageforming apparatus according to claim 13, further comprising a spring,wherein the spring moves in the same direction as the direction ofmovement of the slider.
 15. An image forming apparatus comprising: abelt; a transfer roller to contact with the belt; a supporter to supportthe transfer roller; a connector connected to the supporter by a pin anda slot into which the Din is inserted; a shaft; a spring, the transferroller being biased against the belt by a force of the spring; and aslider to slide from a first position to a second position, the transferroller contacting with the belt when slider is in the first position andthe transfer roller separating from the belt when slider is in thesecond position, wherein the slider moves the spring linearly and causesthe supporter to rotate about the shaft, when the slider slides from thefirst position to the second position.
 16. The image forming apparatusaccording to claim 15, wherein one end of the spring is supported by thesupporter and the other end of the spring is supported by the slider.17. The image forming apparatus according to claim 15, wherein thesupporter includes an arm and a connector connected to the arm.
 18. Theimage forming apparatus according to claim 15, further comprising aneccentric cam to move the slider linearly and a drive motor to drive theeccentric cam.
 19. The image forming apparatus according to claim 15,wherein the transfer roller comes into contact with an inner surface ofthe belt.
 20. The image forming apparatus according to claim 1, whereinthe connector includes the slot, and the arm includes the pin.
 21. Theimage forming apparatus according to claim 1, wherein the slider comesinto contact with the connector by a biasing force of the spring.
 22. Animage forming apparatus comprising: a belt; a transfer roller to comeinto contact with the belt; an arm to rotate about a shaft and tosupport the transfer roller, the arm including an action receivingportion; a connector connected to the arm, the connector includes anaction sending portion to slidably come into contact with the actionreceiving portion; and a spring to press the arm via the actionreceiving portion and the action receiving portion, wherein the actionsending portion slides along the action receiving portion when the armrotates.
 23. The image forming apparatus according to claim 22, whereina distance between the shaft and the action sending portion changes whenthe arm rotates.
 24. The image forming apparatus according to claim 22,wherein the action receiving portion includes a slot, and the actionsending portion includes a pin that is inserted into the slot.